Signaling of adaptive picture size in video bitstream

ABSTRACT

A method of decoding a coded picture of a coded video sequence is performed by at least one processor and the method includes decoding, from a parameter set, a plurality of candidate decoded resolutions, selecting, through an index coded in a transient header structure applicable to a group of samples, a candidate decoded resolution among the plurality of candidate decoded resolutions, resampling a sample of the group of samples based on an output resolution and the selected candidate decoded resolution, and enabling prediction using the resampled sample.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from U.S. Provisional PatentApplication No. 62/816,667, filed on Mar. 11, 2019, in the United StatesPatent and Trademark Office, which is incorporated herein by referencein its entirety.

BACKGROUND 1. Field

The disclosed subject matter relates to video coding and decoding, andmore specifically, to the signaling of picture, or parts of a picture,size that may change from picture to picture or picture part to picturepart.

2. Description of Related Art

Video coding and decoding using inter-picture prediction with motioncompensation has been known for decades. Uncompressed digital video canconsist of a series of pictures, each picture having a spatial dimensionof, for example, 1920×1080 luminance samples and associated chrominancesamples. The series of pictures can have a fixed or variable picturerate (informally also known as frame rate), of, for example 60 picturesper second or 60 Hz. Uncompressed video has significant bitraterequirements. For example, 1080p60 4:2:0 video at 8 bit per sample(1920×1080 luminance sample resolution at 60 Hz frame rate) requiresclose to 1.5 Gbit/s bandwidth. An hour of such video requires more than600 GByte of storage space.

One purpose of video coding and decoding can be the reduction ofredundancy in the input video signal, through compression. Compressioncan help reducing aforementioned bandwidth or storage spacerequirements, in some cases by two orders of magnitude or more. Bothlossless and lossy compression, as well as a combination thereof can beemployed. Lossless compression refers to techniques where an exact copyof the original signal can be reconstructed from the compressed originalsignal. When using lossy compression, the reconstructed signal may notbe identical to the original signal, but the distortion between originaland reconstructed signal is small enough to make the reconstructedsignal useful for the intended application. In the case of video, lossycompression is widely employed. The amount of distortion tolerateddepends on the application; for example, users of certain consumerstreaming applications may tolerate higher distortion than users oftelevision contribution applications. The compression ratio achievablecan reflect that: higher allowable/tolerable distortion can yield highercompression ratios.

A video encoder and decoder can utilize techniques from several broadcategories, including, for example, motion compensation, transform,quantization, and entropy coding, some of which will be introducedbelow.

Historically, video encoders and decoders tended to operate on a givenpicture size that was, in most cases, defined and stayed constant for acoded video sequence (CVS), Group of Pictures (GOP), or a similarmulti-picture timeframe. For example, in MPEG-2, system designs areknown to change the horizontal resolution (and, thereby, the picturesize) dependent on factors such as activity of the scene, but only at Ipictures, hence typically for a GOP. The resampling of referencepictures for use of different resolutions within a CVS is known, forexample, from ITU-T Rec. H.263 Annex P. However, here the picture sizedoes not change, only the reference pictures are being resampled,resulting potentially in only parts of the picture canvas being used (incase of downsampling), or only parts of the scene being captured (incase of upsampling). Further, H.263 Annex Q allows the resampling of anindividual macroblock by a factor of two (in each dimension), upward ordownward. Again, the picture size remains the same. The size of amacroblock is fixed in H.263, and therefore does not need to besignaled.

Changes of picture size in predicted pictures became more mainstream inmodern video coding. For example, VP9 allows reference pictureresampling and change of resolution for a whole picture. Similarly,certain proposals made towards VVC (including, for example, Hendry, et.al, “On adaptive resolution change (ARC) for VVC”, Joint Video Teamdocument WET-M0135-v1, Jan. 9-19, 2019, incorporated herein in itsentirety) allow for resampling of whole reference pictures todifferent—higher or lower—resolutions. In that document, differentcandidate resolutions are suggested to be coded in the sequenceparameter set and referred to by per-picture syntax elements in thepicture parameter set.

SUMMARY

According to embodiments, a method of decoding a coded picture of acoded video sequence is performed by at least one processor and includesdecoding, from a parameter set, a plurality of candidate decodedresolutions, selecting, through an index coded in a transient headerstructure applicable to a group of samples, a candidate decodedresolution among the plurality of candidate decoded resolutions,resampling a sample of the group of samples based on an outputresolution and the selected candidate decoded resolution, and enablingprediction using the resampled sample.

According to embodiments, an apparatus for decoding a coded picture of acoded video sequence, includes at least one memory configured to storecomputer program code, and at least one processor configured to accessthe at least one memory and operate according to the computer programcode, the computer program code including decoding code configured todecode, from a parameter set, a plurality of candidate decodedresolutions, selecting code configured to select, through an index codedin a transient header structure applicable to a group of samples, acandidate decoded resolution among the plurality of candidate decodedresolutions, resampling code configured to resample a sample of thegroup of samples based on an output resolution and the selectedcandidate decoded resolution, and enabling code configured to enableprediction using the resampled sample.

According to embodiments, a non-transitory computer-readable storagemedium storing a program for decoding a coded picture of a coded videosequence includes instructions that cause a processor to decode, from aparameter set, a plurality of candidate decoded resolutions, select,through an index coded in a transient header structure applicable to agroup of samples, a candidate decoded resolution among the plurality ofcandidate decoded resolutions, resample a sample of the group of samplesbased on an output resolution and the selected candidate decodedresolution, and enable prediction using the resampled sample.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1 is a schematic illustration of a simplified block diagram of acommunication system in accordance with an embodiment.

FIG. 2 is a schematic illustration of a simplified block diagram of acommunication system in accordance with an embodiment.

FIG. 3 is a schematic illustration of a simplified block diagram of adecoder in accordance with an embodiment.

FIG. 4 is a schematic illustration of a simplified block diagram of anencoder in accordance with an embodiment.

FIG. 5A is a schematic illustration of options for signaling ARCparameters, as indicated.

FIG. 5B is a schematic illustration of options for signaling ARCparameters in accordance with an embodiment, as indicated.

FIG. 6A is a schematic illustration in accordance with an embodiment.

FIG. 6B is a flowchart illustrating a method of decoding a coded pictureof a coded video sequence, according to an embodiment.

FIG. 6C is a simplified block diagram of an apparatus for controllingdecoding of a video sequence, according to an embodiment.

FIG. 7 is a schematic illustration of a computer system in accordancewith an embodiment.

DETAILED DESCRIPTION

Recently, compressed domain aggregation or extraction of multiplesemantically independent picture parts into a single video picture hasgained some attention. In particular, in the context of, for example,360 coding or certain surveillance applications, multiple semanticallyindependent source pictures (for examples the six cube surface of acube-projected 360 scene, or individual camera inputs in case of amulti-camera surveillance setup) may require separate adaptiveresolution settings to cope with different per-scene activity at a givenpoint in time. In other words, encoders, at a given point in time, maychoose to use different resampling factors for different semanticallyindependent pictures that make up the whole 360 or surveillance scene.When combined into a single picture, that, in turn, requires thatreference picture resampling is performed, and adaptive resolutioncoding signaling is available, for parts of a coded picture.

FIG. 1 illustrates a simplified block diagram of a communication system(100) according to an embodiment of the present disclosure. The system(100) may include at least two terminals (110-120) interconnected via anetwork (150). For unidirectional transmission of data, a first terminal(110) may code video data at a local location for transmission to theother terminal (120) via the network (150). The second terminal (120)may receive the coded video data of the other terminal from the network(150), decode the coded data and display the recovered video data.Unidirectional data transmission may be common in media servingapplications and the like.

FIG. 1 illustrates a second pair of terminals (130, 140) provided tosupport bidirectional transmission of coded video that may occur, forexample, during videoconferencing. For bidirectional transmission ofdata, each terminal (130, 140) may code video data captured at a locallocation for transmission to the other terminal via the network (150).Each terminal (130, 140) also may receive the coded video datatransmitted by the other terminal, may decode the coded data and maydisplay the recovered video data at a local display device.

In FIG. 1, the terminals (110-140) may be illustrated as servers,personal computers and smart phones but the principles of the presentdisclosure may be not so limited. Embodiments of the present disclosurefind application with laptop computers, tablet computers, media playersand/or dedicated video conferencing equipment. The network (150)represents any number of networks that convey coded video data among theterminals (110-140), including for example wireline and/or wirelesscommunication networks. The communication network (150) may exchangedata in circuit-switched and/or packet-switched channels. Representativenetworks include telecommunications networks, local area networks, widearea networks and/or the Internet. For the purposes of the presentdiscussion, the architecture and topology of the network (150) may beimmaterial to the operation of the present disclosure unless explainedherein below.

FIG. 2 illustrates, as an example for an application for the disclosedsubject matter, the placement of a video encoder and decoder in astreaming environment. The disclosed subject matter can be equallyapplicable to other video enabled applications, including, for example,video conferencing, digital TV, storing of compressed video on digitalmedia including CD, DVD, memory stick and the like, and so on.

A streaming system may include a capture subsystem (213), that caninclude a video source (201), for example a digital camera, creating afor example uncompressed video sample stream (202). That sample stream(202), depicted as a bold line to emphasize a high data volume whencompared to encoded video bitstreams, can be processed by an encoder(203) coupled to the camera (201). The encoder (203) can includehardware, software, or a combination thereof to enable or implementaspects of the disclosed subject matter as described in more detailbelow. The encoded video bitstream (204), depicted as a thin line toemphasize the lower data volume when compared to the sample stream, canbe stored on a streaming server (205) for future use. One or morestreaming clients (206, 208) can access the streaming server (205) toretrieve copies (207, 209) of the encoded video bitstream (204). Aclient (206) can include a video decoder (210) which decodes theincoming copy of the encoded video bitstream (207) and creates anoutgoing video sample stream (211) that can be rendered on a display(212) or other rendering device (not depicted). In some streamingsystems, the video bitstreams (204, 207, 209) can be encoded accordingto certain video coding/compression standards. Examples of thosestandards include ITU-T Recommendation H.265. Under development is avideo coding standard informally known as Versatile Video Coding or VVC.The disclosed subject matter may be used in the context of VVC.

FIG. 3 may be a functional block diagram of a video decoder (210)according to an embodiment.

A receiver (310) may receive one or more codec video sequences to bedecoded by the decoder (210); in the same or another embodiment, onecoded video sequence at a time, where the decoding of each coded videosequence is independent from other coded video sequences. The codedvideo sequence may be received from a channel (312), which may be ahardware/software link to a storage device which stores the encodedvideo data. The receiver (310) may receive the encoded video data withother data, for example, coded audio data and/or ancillary data streams,that may be forwarded to their respective using entities (not depicted).The receiver (310) may separate the coded video sequence from the otherdata. To combat network jitter, a buffer memory (315) may be coupled inbetween receiver (310) and entropy decoder/parser (320) (“parser”henceforth). When receiver (310) is receiving data from a store/forwarddevice of sufficient bandwidth and controllability, or from anisosychronous network, the buffer (315) may not be needed, or can besmall. For use on best effort packet networks such as the Internet, thebuffer (315) may be required, can be comparatively large and canadvantageously of adaptive size.

The video decoder (210) may include an parser (320) to reconstructsymbols (321) from the entropy coded video sequence. Categories of thosesymbols include information used to manage operation of the decoder(210), and potentially information to control a rendering device such asa display (212) that is not an integral part of the decoder but can becoupled to it, as was shown in FIG. 2. The control information for therendering device(s) may be in the form of Supplementary EnhancementInformation (SEI messages) or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (320) mayparse/entropy-decode the coded video sequence received. The coding ofthe coded video sequence can be in accordance with a video codingtechnology or standard, including variable length coding, Huffmancoding, arithmetic coding with or without context sensitivity, and soforth. The parser (320) may extract from the coded video sequence, a setof subgroup parameters for at least one of the subgroups of pixels inthe video decoder, based upon at least one parameters corresponding tothe group. Subgroups can include Groups of Pictures (GOPs), pictures,tiles, slices, macroblocks, Coding Units (CUs), blocks, Transform Units(TUs), Prediction Units (PUs) and so forth. The entropy decoder/parsermay also extract from the coded video sequence information such astransform coefficients, quantizer parameter values, motion vectors, andso forth.

The parser (320) may perform entropy decoding/parsing operation on thevideo sequence received from the buffer (315), so to create symbols(321).

Reconstruction of the symbols (321) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by the subgroupcontrol information that was parsed from the coded video sequence by theparser (320). The flow of such subgroup control information between theparser (320) and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, decoder 210 can beconceptually subdivided into a number of functional units as describedbelow. In a practical implementation operating under commercialconstraints, many of these units interact closely with each other andcan, at least partly, be integrated into each other. However, for thepurpose of describing the disclosed subject matter, the conceptualsubdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (351). Thescaler/inverse transform unit (351) receives quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (321) from the parser (320). It can output blockscomprising sample values, that can be input into aggregator (355).

In some cases, the output samples of the scaler/inverse transform (351)can pertain to an intra coded block; that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (352). In some cases, the intra pictureprediction unit (352) generates a block of the same size and shape ofthe block under reconstruction, using surrounding already reconstructedinformation fetched from the current (partly reconstructed) picture(356). The aggregator (355), in some cases, adds, on a per sample basis,the prediction information the intra prediction unit (352) has generatedto the output sample information as provided by the scaler/inversetransform unit (351).

In other cases, the output samples of the scaler/inverse transform unit(351) can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a Motion Compensation Prediction unit (353) canaccess reference picture memory (357) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (321) pertaining to the block, these samples can beadded by the aggregator (355) to the output of the scaler/inversetransform unit (in this case called the residual samples or residualsignal) so to generate output sample information. The addresses withinthe reference picture memory form where the motion compensation unitfetches prediction samples can be controlled by motion vectors,available to the motion compensation unit in the form of symbols (321)that can have, for example X, Y, and reference picture components.Motion compensation also can include interpolation of sample values asfetched from the reference picture memory when sub-sample exact motionvectors are in use, motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (355) can be subject to variousloop filtering techniques in the loop filter unit (354). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video bitstream andmade available to the loop filter unit (354) as symbols (321) from theparser (320), but can also be responsive to meta-information obtainedduring the decoding of previous (in decoding order) parts of the codedpicture or coded video sequence, as well as responsive to previouslyreconstructed and loop-filtered sample values.

The output of the loop filter unit (354) can be a sample stream that canbe output to the render device (212) as well as stored in the referencepicture memory (356) for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. Once a coded picture is fullyreconstructed and the coded picture has been identified as a referencepicture (by, for example, parser (320)), the current reference picture(356) can become part of the reference picture buffer (357), and a freshcurrent picture memory can be reallocated before commencing thereconstruction of the following coded picture.

The video decoder 320 may perform decoding operations according to apredetermined video compression technology that may be documented in astandard, such as ITU-T Rec. H.265. The coded video sequence may conformto a syntax specified by the video compression technology or standardbeing used, in the sense that it adheres to the syntax of the videocompression technology or standard, as specified in the videocompression technology document or standard and specifically in theprofiles document therein. Also necessary for compliance can be that thecomplexity of the coded video sequence is within bounds as defined bythe level of the video compression technology or standard. In somecases, levels restrict the maximum picture size, maximum frame rate,maximum reconstruction sample rate (measured in, for example megasamplesper second), maximum reference picture size, and so on. Limits set bylevels can, in some cases, be further restricted through HypotheticalReference Decoder (HRD) specifications and metadata for HRD buffermanagement signaled in the coded video sequence.

In an embodiment, the receiver (310) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (320) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or SNR enhancementlayers, redundant slices, redundant pictures, forward error correctioncodes, and so on.

FIG. 4 may be a functional block diagram of a video encoder (203)according to an embodiment of the present disclosure.

The encoder (203) may receive video samples from a video source (201)(that is not part of the encoder) that may capture video image(s) to becoded by the encoder (203).

The video source (201) may provide the source video sequence to be codedby the encoder (203) in the form of a digital video sample stream thatcan be of any suitable bit depth (for example: 8 bit, 10 bit, 12 bit, .. . ), any colorspace (for example, BT.601 Y CrCB, RGB, . . . ) and anysuitable sampling structure (for example Y CrCb 4:2:0, Y CrCb 4:4:4). Ina media serving system, the video source (201) may be a storage devicestoring previously prepared video. In a videoconferencing system, thevideo source (203) may be a camera that captures local image informationas a video sequence. Video data may be provided as a plurality ofindividual pictures that impart motion when viewed in sequence. Thepictures themselves may be organized as a spatial array of pixels,wherein each pixel can comprise one or more sample depending on thesampling structure, color space, etc. in use. The description belowfocuses on samples.

According to an embodiment, the encoder (203) may code and compress thepictures of the source video sequence into a coded video sequence (443)in real time or under any other time constraints as required by theapplication. Enforcing appropriate coding speed is one function ofController (450). Controller controls other functional units asdescribed below and is functionally coupled to these units. The couplingis not depicted for clarity. Parameters set by controller can includerate control related parameters (picture skip, quantizer, lambda valueof rate-distortion optimization techniques, . . . ), picture size, groupof pictures (GOP) layout, maximum motion vector search range, and soforth. Other functions of a controller (450) may be performed as theymay pertain to video encoder (203) optimized for a certain systemdesign.

Some video encoders operate in what a person skilled in the are readilyrecognizes as a “coding loop”. As an oversimplified description, acoding loop can consist of the encoding part of an encoder (430)(“source coder” henceforth) (responsible for creating symbols based onan input picture to be coded, and a reference picture(s)), and a (local)decoder (433) embedded in the encoder (203) that reconstructs thesymbols to create the sample data a (remote) decoder also would create(as any compression between symbols and coded video bitstream islossless in the video compression technologies considered in thedisclosed subject matter). That reconstructed sample stream is input tothe reference picture memory (434). As the decoding of a symbol streamleads to bit-exact results independent of decoder location (local orremote), the reference picture buffer content is also bit exact betweenlocal encoder and remote encoder. In other words, the prediction part ofan encoder “sees” as reference picture samples exactly the same samplevalues as a decoder would “see” when using prediction during decoding.This is a principle of reference picture synchronicity (and resultingdrift, if synchronicity cannot be maintained, for example because ofchannel errors).

The operation of the “local” decoder (433) can be the same as of a“remote” decoder (210), which has already been described in detail abovein conjunction with FIG. 3. Briefly referring also to FIG. 3, however,as symbols are available and en/decoding of symbols to a coded videosequence by entropy coder (445) and parser (320) can be lossless, theentropy decoding parts of decoder (210), including channel (312),receiver (310), buffer (315), and parser (320) may not be fullyimplemented in local decoder (433).

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that is present in adecoder also necessarily needs to be present, in substantially identicalfunctional form, in a corresponding encoder. For this reason, thedisclosed subject matter focuses on decoder operation. The descriptionof encoder technologies can be abbreviated as they are the inverse ofthe comprehensively described decoder technologies. Only in certainareas a more detail description is required and provided below.

As part of its operation, the source coder (430) may perform motioncompensated predictive coding, which codes an input frame predictivelywith reference to one or more previously-coded frames from the videosequence that were designated as “reference frames.” In this manner, thecoding engine (432) codes differences between pixel blocks of an inputframe and pixel blocks of reference frame(s) that may be selected asprediction reference(s) to the input frame.

The local video decoder (433) may decode coded video data of frames thatmay be designated as reference frames, based on symbols created by thesource coder (430). Operations of the coding engine (432) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 4), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (433) replicates decodingprocesses that may be performed by the video decoder on reference framesand may cause reconstructed reference frames to be stored in thereference picture cache (434). In this manner, the encoder (203) maystore copies of reconstructed reference frames locally that have commoncontent as the reconstructed reference frames that will be obtained by afar-end video decoder (absent transmission errors).

The predictor (435) may perform prediction searches for the codingengine (432). That is, for a new frame to be coded, the predictor (435)may search the reference picture memory (434) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(435) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (435), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (434).

The controller (450) may manage coding operations of the video coder(430), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (445). The entropy coder translatesthe symbols as generated by the various functional units into a codedvideo sequence, by loss-less compressing the symbols according tovarious technologies, for example Huffman coding, variable lengthcoding, arithmetic coding, and so forth.

The transmitter (440) may buffer the coded video sequence(s) as createdby the entropy coder (445) to prepare it for transmission via acommunication channel (460), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(440) may merge coded video data from the video coder (430) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (450) may manage operation of the encoder (203). Duringcoding, the controller (450) may assign to each coded picture a certaincoded picture type, which may affect the coding techniques that may beapplied to the respective picture. For example, pictures often may beassigned as one of the following frame types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other frame in the sequence as a source of prediction.Some video codecs allow for different types of Intra pictures,including, for example Independent Decoder Refresh Pictures. Variants ofI pictures and their respective applications and features may beemployed.

A Predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A Bi-directionally Predictive Picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded non-predictively,via spatial prediction or via temporal prediction with reference to onepreviously coded reference pictures. Blocks of B pictures may be codednon-predictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video coder (203) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video coder (203) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (440) may transmit additional datawith the encoded video. The video coder (430) may include such data aspart of the coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, Supplementary EnhancementInformation (SEI) messages, Visual Usability Information (VUI) parameterset fragments, and so on.

Before describing certain aspects of the disclosed subject matter inmore detail, a few terms need to be introduced that will be referred toin the remainder of this description.

Sub-Picture henceforth refers to an, in some cases, rectangulararrangement of samples, blocks, macroblocks, coding units, or similarentities that are semantically grouped, and that may be independentlycoded in changed resolution. One or more sub-pictures may for a picture.One or more coded sub-pictures may form a coded picture. One or moresub-pictures may be assembled into a picture, and one or more subpictures may be extracted from a picture. In certain environments, oneor more coded sub-pictures may be assembled in the compressed domainwithout transcoding to the sample level into a coded picture, and in thesame or certain other cases, one or more coded sub-pictures may beextracted from a coded picture in the compressed domain.

Adaptive Resolution Change (ARC) henceforth refers to mechanisms thatallow the change of resolution of a picture or sub-picture within acoded video sequence, by the means of, for example, reference pictureresampling. ARC parameters may refer to the types of control informationrequired to perform adaptive resolution change, that may include, forexample, filter parameters, scaling factors, resolutions of outputand/or reference pictures, various control flags, and so forth. Thus,ARC information may refer to data and values corresponding to the ARCparameters.

Above description is focused on coding and decoding a single,semantically independent coded video picture. Before describing theimplication of coding/decoding of multiple sub pictures with independentARC parameters and its implied additional complexity, options forsignaling ARC parameters shall be described.

Referring to FIG. 5A, shown are several novel options for signaling ARCparameters. As noted with each of the options, they have certainadvantages and certain disadvantages from a coding efficiency,complexity, and architecture viewpoint. A video coding standard ortechnology may choose one or more of these options, or other options,for signaling ARC parameters. The options may not be mutually exclusive,and conceivably may be interchanged based on application needs,standards technology involved, or encoder's choice.

Classes of ARC parameters may include:

-   -   up/downsample factors, separate or combined in X and Y dimension    -   up/downsample factors, with an addition of a temporal dimension,        indicating constant speed zoom in/out for a given number of        pictures    -   Either of the above two may involve the coding of one or more        presumably short syntax elements that may point into a table        containing the factor(s).    -   resolution, in X or Y dimension, in units of samples, blocks,        macroblocks, CUs, or any other suitable granularity, of the        input picture, output picture, reference picture, coded picture,        combined or separately. If there is more than one resolution        (such as, for example, one for input picture, one for reference        picture) then, in certain cases, one set of values may be        inferred to from another set of values. Such could be gated, for        example, by the use of flags. For a more detailed example, see        below.    -   “warping” coordinates akin those used in H.263 Annex P, again in        a suitable granularity as described above. H.263 Annex P defines        one efficient way to code such warping coordinates, but other,        potentially more efficient ways could conceivably also be        devised. For example, the variable length reversible,        “Huffman”-style coding of warping coordinates of Annex P could        be replaced by a suitable length binary coding, where the length        of the binary code word could, for example, be derived from a        maximum picture size, possibly multiplied by a certain factor        and offset by a certain value, so to allow for “warping” outside        of the maximum picture size's boundaries.    -   up or downsample filter parameters. In the easiest case, there        may be only a single filter for up and/or downsampling. However,        in certain cases, it can be advantageous to allow more        flexibility in filter design, and that may require to signaling        of filter parameters. Such parameters may be selected through an        index in a list of possible filter designs, the filter may be        fully specified (for example through a list of filter        coefficients, using suitable entropy coding techniques), the        filter may be implicitly selected through up/downsample ratios        according which in turn are signaled according to any of the        mechanisms mentioned above, and so forth.

Henceforth, the description assumes the coding of a finite set ofup/downsample factors (the same factor to be used in both X and Ydimension), indicated through a codeword. That codeword canadvantageously be variable length coded, for example using theExp-Golomb code common for certain syntax elements in video codingspecifications such as H.264 and H.265. One suitable mapping of valuesto up/downsample factors can, for example, be according to the followingtable

Codeword Exp-Golomb Code Original/Target resolution 0 1 1/1 1 010 1/1.5(upscale by 50%) 2 011 1.5/1 (downscale by 50%) 3 00100 1/2 (upscale by100%) 4 00101 2/1 (downscale by 100%)

Many similar mappings could be devised according to the needs of anapplication and the capabilities of the up and downscale mechanismsavailable in a video compression technology or standard. The table couldbe extended to more values. Values may also be represented by entropycoding mechanisms other than Exp-Golomb codes, for example using binarycoding. That may have certain advantages when the resampling factorswere of interest outside the video processing engines (encoder anddecoder foremost) themselves, for example by MANEs. It should be notedthat, for the (presumably) most common case where no resolution changeis required, an Exp-Golomb code can be chosen that is short; in thetable above, only a single bit. That can have a coding efficiencyadvantage over using binary codes for the most common case.

The number of entries in the table, as well as their semantics may befully or partially configurable. For example, the basic outline of thetable may be conveyed in a “high” parameter set such as a sequence ordecoder parameter set. Alternatively or in addition, one or more suchtables may be defined in a video coding technology or standard, and maybe selected through for example a decoder or sequence parameter set.

Henceforth, we describe how an upsample/downsample factor (ARCinformation), coded as described above, may be included in a videocoding technology or standard syntax. Similar considerations may applyto one, or a few, codewords controlling up/downsample filters. See belowfor a discussion when comparatively large amounts of data are requiredfor a filter or other data structures.

H.263 Annex P includes the ARC information 502 in the form of fourwarping coordinates into the picture header 501, specifically in theH.263 PLUSPTYPE (503) header extension. This form of ARC information 502can be used when a) there is a picture header available, and b) frequentchanges of the ARC information are expected. However, the overhead whenusing H.263-style signaling can be quite high, and scaling factors maynot pertain among picture boundaries as picture header can be oftransient nature.

JVCET-M135-v1, cited above, includes the ARC reference information (505)(an index) located in a picture parameter set (504), indexing a table(506) including target resolutions that in turn is located inside asequence parameter set (507). The placement of the possible resolutionin a table (506) in the sequence parameter set (507) can, according toverbal statements made by the authors, be justified by using the SPS asan interoperability negotiation point during capability exchange.Resolution can change, within the limits set by the values in the table(506) from picture to picture by referencing the appropriate pictureparameter set (504).

The following additional options may exist to convey ARC information ina video bitstream. Each of those options has certain advantages asdescribed above. The options may be simultaneously present in the samevideo coding technology or standard.

In an embodiment illustrated in FIG. 5B, ARC information (509) such as aresampling (zoom) factor may be present in a slice header, GOB header,tile header, or tile group header (tile group header henceforth) (508).This can be adequate of the ARC information is small, such as a singlevariable length ue(v) or fixed length codeword of a few bits, forexample as shown above. Having the ARC information in a tile groupheader directly has the additional advantage of the ARC information maybe applicable to a sub picture represented by, for example, that tilegroup, rather than the whole picture. See also below. In addition, evenif the video compression technology or standard envisions only wholepicture adaptive resolution changes (in contrast to, for example, tilegroup based adaptive resolution changes), putting the ARC informationinto the tile group header vis a vis putting it into an H.263-stylepicture header has certain advantages from an error resilienceviewpoint.

In the same or another embodiment, the ARC information (512) itself maybe present in an appropriate parameter set (511) such as, for example, apicture parameter set, header parameter set, tile parameter set,adaptation parameter set, and so forth (Adaptation parameter setdepicted). The scope of that parameter set can advantageously be nolarger than a picture, for example a tile group. The use of the ARCinformation is implicit through the activation of the relevant parameterset. For example, when a video coding technology or standardcontemplates only picture-based ARC, then a picture parameter set orequivalent may be appropriate.

In the same or another embodiment, ARC reference information (513) maybe present in a Tile Group header (514) or a similar data structure.That reference information (513) can refer to a subset of ARCinformation (515) available in a parameter set (516) with a scope beyonda single picture, for example a sequence parameter set, or decoderparameter set.

The additional level of indirection implied activation of a pictureparameter set (PPS) from a tile group header, PPS, sequence parameterset (SPS), as used in WET-M0135-v1 appears to be unnecessary, as pictureparameter sets, just as sequence parameter sets, can (and have incertain standards such as RFC3984) be used for capability negotiation orannouncements. A PPS generally refers to a syntax structure containingsyntax elements that apply to zero or more entire coded pictures asdetermined by a syntax element found in each slice header. A SPSgenerally refers to a syntax structure containing syntax elements thatapply to zero or more entire coded layer video sequences (CLVSs) asdetermined by the content of a syntax element found in the PPS referredto by a syntax element found in each picture header. If, however, theARC information should be applicable to a sub picture represented, forexample, by a tile groups also, a parameter set with an activation scopelimited to a tile group, such as the Adaptation Parameter set or aHeader Parameter Set may be the better choice. Also, if the ARCinformation is of more than negligible size—for example contains filtercontrol information such as numerous filter coefficients—then aparameter may be a better choice than using a header (508) directly froma coding efficiency viewpoint, as those settings may be reusable byfuture pictures or sub-pictures by referencing the same parameter set.

When using the sequence parameter set or another higher parameter setwith a scope spanning multiple pictures, certain considerations mayapply:

-   -   1. The parameter set to store the ARC information table (516)        can, in some cases, be the sequence parameter set, but in other        cases advantageously the decoder parameter set. The decoder        parameter set can have an activation scope of multiple CVSs,        namely the coded video stream, i.e. all coded video bits from        session start until session teardown. Such a scope may be more        appropriate because possible ARC factors may be a decoder        feature, possibly implemented in hardware, and hardware features        tend not to change with any CVS (which in at least some        entertainment systems is a Group of Pictures, one second or less        in length). That said, putting the table into the sequence        parameter set is expressly included in the placement options        described herein, in particular in conjunction with point 2        below.    -   2. The ARC reference information (513) may advantageously be        placed directly into the picture/slice tile/GOB/tile group        header (tile group header henceforth) (514) rather than into the        picture parameter set as in JVCET-M0135-v1. The reason is as        follows: when an encoder wants to change a single value in a        picture parameter set, such as for example the ARC reference        information, then it has to create a new PPS and reference that        new PPS. Assume that only the ARC reference information changes,        but other information such as, for example, the quantization        matrix information in the PPS stays. Such information can be of        substantial size, and would need to be retransmitted to make the        new PPS complete. As the ARC reference information may be a        single codeword, such as the index into the table (513) and that        would be the only value that changes, it would be cumbersome and        wasteful to retransmit all the, for example, quantization matrix        information. Insofar, can be considerably better from a coding        efficiency viewpoint to avoid the indirection through the PPS,        as proposed in JVET-M0135-v1. Similarly, putting the ARC        reference information into the PPS has the additional        disadvantage that the ARC information referenced by the ARC        reference information (513) necessarily needs to apply to the        whole picture and not to a sub-picture, as the scope of a        picture parameter set activation is a picture.

In the same or another embodiment, the signaling of ARC parameters canfollow a detailed example as outlined in FIG. 6A. FIG. 6A depicts syntaxdiagrams in a representation as used in video coding standards since atleast 1993. The notation of such syntax diagrams roughly follows C-styleprogramming. Lines in boldface indicate syntax elements present in thebitstream, lines without boldface often indicate control flow or thesetting of variables.

A tile group header (601) as an example syntax structure of a headerapplicable to a (possibly rectangular) part of a picture canconditionally contain, a variable length, Exp-Golomb coded syntaxelement dec_pic_size_idx (602) (depicted in boldface). The presence ofthis syntax element in the tile group header can be gated on the use ofadaptive resolution (603)—here, the value of a flag not depicted inboldface, which means that flag is present in the bitstream at the pointwhere it occurs in the syntax diagram. Whether or not adaptiveresolution is in use for this picture or parts thereof can be signaledin any high level syntax structure inside or outside the bitstream. Inthe example shown, it is signaled in the sequence parameter set asoutlined below.

Still referring to FIG. 6A, shown is also an excerpt of a sequenceparameter set (610). The first syntax element shown isadaptive_pic_resolution_change_flag (611). When true, that flag canindicate the use of adaptive resolution which, in turn may requirecertain control information. In the example, such control information isconditionally present based on the value of the flag based on the if( )statement in the parameter set (612) and the tile group header (601).

When adaptive resolution is in use, in this example, coded is an outputresolution in units of samples (613). The numeral 613 refers to bothoutput_pic_width_in_luma_samples and output_pic_height_in_luma_samples,which together can define the resolution of the output picture.Elsewhere in a video coding technology or standard, certain restrictionsto either value can be defined. For example, a level definition maylimit the number of total output samples, which could be the product ofthe value of those two syntax elements. Also, certain video codingtechnologies or standards, or external technologies or standards suchas, for example, system standards, may limit the numbering range (forexample, one or both dimensions must be divisible by a power of 2number), or the aspect ratio (for example, the width and height must bein a relation such as 4:3 or 16:9). Such restrictions may be introducedto facilitate hardware implementations or for other reasons.

In certain applications, it can be advisable that the encoder instructsthe decoder to use a certain reference picture size rather thanimplicitly assume that size to be the output picture size. In thisexample, the syntax element reference_pic_size_present_flag (614) gatesthe conditional presence of reference picture dimensions (615) (again,the numeral refers to both width and height).

Finally, shown is a table of possible decoding picture width andheights. Such a table can be expressed, for example, by a tableindication (num_dec_pic_size_in_luma_samples_minus1) (616). The “minus1”can refer to the interpretation of the value of that syntax element. Forexample, if the coded value is zero, one table entry is present. If thevalue is five, six table entries are present. For each “line” in thetable, decoded picture width and height are then included in the syntax(617).

The table entries presented (617) can be indexed using the syntaxelement decpic_size_idx (602) in the tile group header, thereby allowingdifferent decoded sizes—in effect, zoom factors—per tile group.

Certain video coding technologies or standards, for example VP9, supportspatial scalability by implementing certain forms of reference pictureresampling (signaled quite differently from the disclosed subjectmatter) in conjunction with temporal scalability, so to enable spatialscalability. In particular, certain reference pictures may be upsampledusing ARC-style technologies to a higher resolution to form the base ofa spatial enhancement layer. Those upsampled pictures could be refined,using normal prediction mechanisms at the high resolution, so to adddetail.

The disclosed subject matter can be used in such an environment. Incertain cases, in the same or another embodiment, a value in the NALunit header, for example the Temporal ID field, can be used to indicatenot only the temporal but also the spatial layer. Doing so has certainadvantages for certain system designs; for example, Selected ForwardingUnits (SFU) created and optimized for temporal layer selected forwardingbased on the NAL unit header Temporal ID value can be used withoutmodification, for scalable environments. In order to enable that, theremay be a requirement for a mapping between the coded picture size andthe temporal layer is indicated by the temporal ID field in the NAL unitheader.

FIG. 6B is a flowchart illustrating a method (620) of decoding a codedpicture of a coded video sequence, according to an embodiment. In someimplementations, one or more process blocks of FIG. 6B may be performedby the decoder (210). In some implementations, one or more processblocks of FIG. 6B may be performed by another device or a group ofdevices separate from or including the decoder (210), such as theencoder (203).

Referring to FIG. 6B, the method (620) includes determining whether ARCinformation is available (621), and if it is determined that ARCinformation is not available then the method ends (650). If it isdetermined that ARC information is available, then the method includesdecoding, from a parameter set, a plurality of candidate decodedresolutions (625).

The method (620) includes selecting, through an index coded in atransient header structure applicable to a group of samples, a candidatedecoded resolution among the plurality of candidate decoded resolutions(630).

The method (620) includes resampling a sample of the group of samplesbased on an output resolution and the selected candidate decodedresolution (635).

The method (620) includes enabling prediction using the resampled sample(640).

The method (620) may further include wherein the transient headerstructure is any one or any combination of a picture header, a tilegroup header, a tile header, a slice header, and a Group of Blocksheader.

The method (620) may further include wherein the index is coded in anExp-Golomb code.

The method (620) may further include wherein the transient headerstructure is the tile group header and the tile group header comprises aresampling factor.

The method (620) may further include wherein the transient headerstructure is the tile group header and the tile group header comprisesadaptive resolution change (ARC) reference information.

The method (620) may further include wherein the ARC referenceinformation refers to a subset of ARC information available in aparameter set.

The method (620) may further include wherein a number of the candidatedecoded resolutions is coded in an Exp-Golomb code coded syntax elementpreceding the plurality of candidate decoded resolutions.

Although FIG. 6B shows example blocks of the method (620), in someimplementations, the method (620) may include additional blocks, fewerblocks, different blocks, or differently arranged blocks than thosedepicted in FIG. 6B. Additionally, or alternatively, two or more of theblocks of the method (620) may be performed in parallel.

Further, the proposed methods may be implemented by processing circuitry(e.g., one or more processors or one or more integrated circuits). In anexample, the one or more processors execute a program that is stored ina non-transitory computer-readable medium to perform one or more of theproposed methods.

FIG. 6C is a simplified block diagram of an apparatus (660) for decodinga coded picture of a video sequence, according to an embodiment.

Referring to FIG. 6C, the apparatus (660) includes decoding code (670),selecting code (675), resampling code (680), and enabling code (685).

The decoding code (670) is configured to decode, from a parameter set, aplurality of candidate decoded resolutions.

The selecting code (675) is configured to select, through an index codedin a transient header structure applicable to a group of samples, acandidate decoded resolution among the plurality of candidate decodedresolutions.

The resampling code (680) is configured to resample a sample of thegroup of samples based on an output resolution and the selectedcandidate decoded resolution.

The enabling code (685) is configured to enable prediction using theresampled sample.

The techniques for signaling adaptive resolution parameters describedabove, can be implemented as computer software using computer-readableinstructions and physically stored in one or more computer-readablemedia. For example, FIG. 7 shows a computer system 700 suitable forimplementing certain embodiments of the disclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by computer central processing units (CPUs),Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 7 for computer system 700 are exemplary innature and are not intended to suggest any limitation as to the scope ofuse or functionality of the computer software implementing embodimentsof the present disclosure. Neither should the configuration ofcomponents be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in anembodiment of a computer system 700.

Computer system 700 may include certain human interface input devices.Such a human interface input device may be responsive to input by one ormore human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard 701, mouse 702, trackpad 703, touch screen 710,data-glove 704, joystick 705, microphone 706, scanner 707, camera 708.

Computer system 700 may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen 710, data-glove 704, or joystick 705, but there can also betactile feedback devices that do not serve as input devices), audiooutput devices (such as: speakers 709, headphones (not depicted)),visual output devices (such as screens 710 to include CRT screens, LCDscreens, plasma screens, OLED screens, each with or without touch-screeninput capability, each with or without tactile feedback capability—someof which may be capable to output two dimensional visual output or morethan three dimensional output through means such as stereographicoutput; virtual-reality glasses (not depicted), holographic displays andsmoke tanks (not depicted)), and printers (not depicted).

Computer system 700 can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW720 with CD/DVD or the like media 721, thumb-drive 722, removable harddrive or solid state drive 723, legacy magnetic media such as tape andfloppy disc (not depicted), specialized ROM/ASIC/PLD based devices suchas security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system 700 can also include interface to one or morecommunication networks (755). Networks (755) can for example bewireless, wireline, optical. Networks (755) can further be local,wide-area, metropolitan, vehicular and industrial, real-time,delay-tolerant, and so on. Examples of networks (755) include local areanetworks such as Ethernet, wireless LANs, cellular networks to includeGSM, 3G, 4G, 5G, LTE and the like, TV wireline or wireless wide areadigital networks to include cable TV, satellite TV, and terrestrialbroadcast TV, vehicular and industrial to include CANBus, and so forth.Certain networks (755) commonly require external network interfaceadapters (754) that attached to certain general purpose data ports orperipheral buses (749) (such as, for example USB ports of the computersystem 700; others are commonly integrated into the core of the computersystem 700 by attachment to a system bus as described below (for exampleEthernet interface into a PC computer system or cellular networkinterface into a smartphone computer system). Using any of thesenetworks (755), computer system 700 can communicate with other entities.Such communication can be uni-directional, receive only (for example,broadcast TV), uni-directional send-only (for example CANbus to certainCANbus devices), or bi-directional, for example to other computersystems using local or wide area digital networks. Certain protocols andprotocol stacks can be used on each of those networks (755) and networkinterfaces (754) as described above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces (754) can be attached to a core 740 ofthe computer system 700.

The core 740 can include one or more Central Processing Units (CPU) 741,Graphics Processing Units (GPU) 742, specialized programmable processingunits in the form of Field Programmable Gate Areas (FPGA) 743, hardwareaccelerators for certain tasks 744, and so forth. These devices, alongwith Read-only memory (ROM) 745, Random-access memory 746, GraphicsAdapter 750, internal mass storage such as internal non-user accessiblehard drives, SSDs, and the like 747, may be connected through a systembus 748. In some computer systems, the system bus 748 can be accessiblein the form of one or more physical plugs to enable extensions byadditional CPUs, GPU, and the like. The peripheral devices can beattached either directly to the core's system bus 748, or through aperipheral bus 749. Architectures for a peripheral bus include PCI, USB,and the like.

CPUs 741, GPUs 742, FPGAs 743, and accelerators 744 can execute certaininstructions that, in combination, can make up the aforementionedcomputer code. That computer code can be stored in ROM 745 or RAM 746.Transitional data can be also be stored in RAM 746, whereas permanentdata can be stored for example, in the internal mass storage 747. Faststorage and retrieve to any of the memory devices can be enabled throughthe use of cache memory, that can be closely associated with one or moreCPU 741, GPU 742, mass storage 747, ROM 745, RAM 746, and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind known tothose having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture 700, and specifically the core 740 can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core 740 that are of non-transitorynature, such as core-internal mass storage 747 or ROM 745. The softwareimplementing various embodiments of the present disclosure can be storedin such devices and executed by core 740. A computer-readable medium caninclude one or more memory devices or chips, according to particularneeds. The software can cause the core 740 and specifically theprocessors therein (including CPU, GPU, FPGA, and the like) to executeparticular processes or particular parts of particular processesdescribed herein, including defining data structures stored in RAM 746and modifying such data structures according to the processes defined bythe software. In addition or as an alternative, the computer system canprovide functionality as a result of logic hardwired or otherwiseembodied in a circuit (for example: accelerator 744), which can operatein place of or together with software to execute particular processes orparticular parts of particular processes described herein. Reference tosoftware can encompass logic, and vice versa, where appropriate.Reference to a computer-readable media can encompass a circuit (such asan integrated circuit (IC)) storing software for execution, a circuitembodying logic for execution, or both, where appropriate. The presentdisclosure encompasses any suitable combination of hardware andsoftware.

While this disclosure has described several example embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

What is claimed is:
 1. A method of decoding a coded picture of a codedvideo sequence, the method being performed by at least one processor andthe method comprising: decoding, from a parameter set, a plurality ofcandidate decoded resolutions; selecting, through an index coded in atransient header structure applicable to a group of samples, a candidatedecoded resolution among the plurality of candidate decoded resolutions;resampling a sample of the group of samples based on an outputresolution and the selected candidate decoded resolution; and enablingprediction using the resampled sample based on meta-information obtainedduring decoding of previous parts of the coded picture or coded videosequence and previously reconstructed and loop-filtered sample values.2. The method of claim 1, wherein the transient header structure is anyone or any combination of a picture header, a tile group header, a tileheader, a slice header, and a Group of Blocks header.
 3. The method ofclaim 2, wherein the index is coded in an Exp-Golomb code.
 4. The methodof claim 2, wherein the transient header structure is the tile groupheader and the tile group header comprises a resampling factor.
 5. Themethod of claim 2, wherein the transient header structure is the tilegroup header and the tile group header comprises adaptive resolutionchange (ARC) reference information.
 6. The method of claim 5, whereinthe ARC reference information refers to a subset of ARC informationavailable in a parameter set.
 7. The method of claim 1, wherein a numberof the candidate decoded resolutions is coded in an Exp-Golomb codecoded syntax element preceding the plurality of candidate decodedresolutions.
 8. An apparatus for decoding a coded picture of a codedvideo sequence, the apparatus comprising: at least one memory configuredto store computer program code; and at least one processor configured toaccess the at least one memory and operate according to the computerprogram code, the computer program code comprising: decoding codeconfigured to cause the at least one processor to decode, from aparameter set, a plurality of candidate decoded resolutions; selectingcode configured to cause the at least one processor to select, throughan index coded in a transient header structure applicable to a group ofsamples, a candidate decoded resolution among the plurality of candidatedecoded resolutions; resampling code configured to cause the at leastone processor to resample a sample of the group of samples based on anoutput resolution and the selected candidate decoded resolution; andenabling code configured to cause the at least one processor to enableprediction using the resampled sample based on meta-information obtainedduring decoding of previous parts of the coded picture or coded videosequence and previously reconstructed and loop-filtered sample values.9. The apparatus of claim 8, wherein the transient header structure isany one or any combination of a picture header, a tile group header, atile header, a slice header, and a Group of Blocks header.
 10. Theapparatus of claim 9, wherein the index is coded in an Exp-Golomb code.11. The apparatus of claim 9, wherein the transient header structure isthe tile group header and the tile group header comprises a resamplingfactor.
 12. The apparatus of claim 9, wherein the transient headerstructure is the tile group header and the tile group header comprisesadaptive resolution change (ARC) reference information.
 13. Theapparatus of claim 12, wherein the ARC reference information refers to asubset of ARC information available in a parameter set.
 14. Theapparatus of claim 8, wherein a number of the candidate decodedresolutions is coded in an Exp-Golomb code coded syntax elementpreceding the plurality of candidate decoded resolutions.
 15. Anon-transitory computer-readable storage medium storing a program fordecoding a coded picture of a coded video sequence, the programcomprising instructions that cause a processor to: decode, from aparameter set, a plurality of candidate decoded resolutions; select,through an index coded in a transient header structure applicable to agroup of samples, a candidate decoded resolution among the plurality ofcandidate decoded resolutions; resample a sample of the group of samplesbased on an output resolution and the selected candidate decodedresolution; and enable prediction using the resampled sample based onmeta-information obtained during decoding of previous parts of the codedpicture or coded video sequence and previously reconstructed andloop-filtered sample values.
 16. The non-transitory computer-readablestorage medium of claim 15, wherein the transient header structure isany one or any combination of a picture header, a tile group header, atile header, a slice header, and a Group of Blocks header.
 17. Thenon-transitory computer-readable storage medium of claim 16, wherein theindex is coded in an Exp-Golomb code.
 18. The non-transitorycomputer-readable storage medium of claim 16, wherein the transientheader structure is the tile group header and the tile group headercomprises a resampling factor.
 19. The non-transitory computer-readablestorage medium of claim 16, wherein the transient header structure isthe tile group header and the tile group header comprises adaptiveresolution change (ARC) reference information.
 20. The non-transitorycomputer-readable storage medium of claim 15, wherein a number of thecandidate decoded resolutions is coded in an Exp-Golomb code codedsyntax element preceding the plurality of candidate decoded resolutions.